The present invention relates generally to a seal used for a structural cable, and more particularly, to a seal used for sealing an anchor device of a cable to a structural element of a construction work.
In such construction work, for example, cable-stayed bridges, suspension bridges or the like, a structural cable, subjected to tension loadings, connects a top portion of the towers of these bridges to their decks via their anchor devices.
The anchor devices of the structural cable, situated on the top portions of the towers and/or at the level of the decks, serve to transmit tensile loads from the cable to the structure of the construction work. The portions of the towers and deck to which the anchor devices are connected have in many case a hollow structure, the volume inside of such hollow structure is normally hermetic in order to protect the inside volume from external environmental conditions, especially from humidity in order to prevent corrosion of metal structures and/or equipment, such as the anchor devices of the structural cable, inside the hollow structure of the decks and/or the towers of the bridge.
The corrosion protection of the volume inside of the hollow structure is commonly performed by dehumidification of the air contained inside in a way known in the art, for example by maintaining a humidity of air less than 40% to prevent effectively the corrosion of metal. Furthermore, to better limit the corrosion over a long period, the hollow structures should be as hermetic as possible in order to prevent the penetration of moisture from the outside of the hollow structures.
In the case of a stayed-cable bridge as shown in FIG. 1, each stayed cable 2 for supporting a bridge deck 1 is anchored respectively by an anchor device 4 to the deck at point D and to the top portion of the tower 3 at point T, with the details of the anchor device as shown in FIG. 2. The anchor region of the deck and/or of the tower has a hollow structure and a wall 5 of the hollow structure is traversed at many places by the stayed cables which are all singular points needed to be sealed. Because the cables are movable at the level of an opening 6 of the wall 5, variations of loads, movements of the structure and vibrations of the cable will complicate sealing problem, especially in the case where the stayed cable has a plurality of parallel strands 7 sheathed or not, as shown in FIG. 2.
To prevent the penetration of moisture inside the hollow structure, an intuitive solution is to extend continually the natural boundary that is the wall 5 of the hollow structure around the stayed cable, to the centre of the opening through which passes the stayed cable, even between the strands 7 of the stayed cable. For example, the space between the parallel strands 7 can be filled with a soft and sticky product, such as a type of silicone seal.
The realization of this boundary is difficult, as one must remove the strands under tension to inject silicone into the interstices, and it is very difficult to be sure that all voids between the strands are effectively filled. Furthermore, the maintenance of the cable structure having such a sealing system is very difficult. When replacing a strand, for example, the sealing system is typically damaged, because sealing product is torn during intervention on the strand.
Another solution is to place the entire anchor device and thus all of the stayed cable outside the dehumidified zone but inside of the hollow structure. This solution has the disadvantage that the anchor device and the supporting structure of the anchor device, typically formed of metal, cannot benefit from the highly effective corrosion protection of dehumidification inside of the hollow structure.
It is an object of the present invention to solve the above-described problems and to provide an improved sealing system and method for the anchor device of a structural cable in a construction work.